The system described in co-pending UK Pat. No. 2165728, which corresponds to U.S. application Ser. No. 771,245 now U. S. Pat. No. 4,775,858, (incorporated herein by reference) and shown in FIG. 1 is capable of producing a high resolution image whilst simultaneously allowing the operator to view a low resolution version of the image on a color television monitor. The operator creates the image by `drawing` on touch tablet 2 with a stylus and choosing a color and notional implement using keyboard 1. The touch tablet produces signals representing the co-ordinates of the point of contact between the touch tablet and the stylus and these signals are translated to frame store addresses by computer 3. For each picture point designated luminance and chrominance video signals for that and several neighbouring picture points (called a patch) are processed. The number of picture points in each patch and the distribution of chrominance or luminance signals for these points is pre-determined for each type of notional implement which may be chosen. On chosing an implement using the key board signals representing the distribution are stored on the shape RAM 4. Video signals representing the chosen color are stored at corresponding picture points in the patch RAM 5. To obtain the image, each picture point video signal in a patch from 5 is processed in the processor 6 with the signal from that address in the frame store 7, the distribution signal from RAM 4 being used to determine the proportions of new and stored information which will make up the processed signal. The contents of the frame store 7 are read periodically to a television display system 8, to produce a picture of the image. The frame store has sufficient storage locations to store signals for each image point in a picture conforming to TV standards in resolution. The distribution is provided to simulate the effect of the implement on paper. This type of processing is described in our co-pending UK Pat. No. 2089625, which corresponds to U.S. Pat. No. 4,514, 818 (incorporated herein by reference).
The system for producing high resolution images shown in FIG. 1 is divided into two parts, one working at high resolution and one at lower resolution. The processors 6 and 18 in both parts are the same and operate at a rate of 700,000 pixels per second and this enables the low resolution part to operate so that the image appears on the screen of display 8 as the operator draws it which is usually a conventional color T.V. monitor. The frame store 19 in the high resolution part is typically capable of storing 2560 by 2048 picture points which is approximately thirteen times that of the frame store in the low resolution part. The number of picture points in the frame store 19 is much larger than in frame store 7 and each patch associated with a designated picture point will include many more picture points and so there will be more picture points to be processed for each designated address and the processing tends to lag behind that in the low resolution part. The processor is unable to process the signals at the rate required to keep up with the command signals from computer 3 for all rates of `drawing` by the artist and so a buffer store 15 is provided to store these signals.
The signals from keyboard 1 and touch tablet 2 are received by the computer 3 where they are translated to give addresses, patch size and distribution signals to be used in the processing. In the high resolution part of the system the number of picture points in a patch will be greater than in the low resolution part but the shape of the distribution will be the same. The signals from the computer are output to address generator 9, which generates the patch of addresses as required by frame store 7, patch RAM 5, shape RAM 4 and buffer store 15. The patch RAM 5 produces the picture point video signals for the addresses generated by address generator 9. The picture point video signals from patch RAM 5 are processed with corresponding picture point signals from frame store 7 to give a picture on display 8 in approximately real time, i.e. as the operator draws a line it will appear on the screen blending with any picture information previously in the store 7 for the same addresses. The image produced on the screens will closely simulate the effects expected if the operator were using real painting equipment such as paper and pens. Unless the processing in the high resolution part of the system is keeping up with the input commands these will be held in the buffer store 15 until the processor 18 is able to process the patch of picture point signals surrounding the designated signal. However, the operator is able to continue creating the image in his own time, since he is able to observe the effect he is creating by observing the low resolution display at 8, although he can not observe the high definition picture whilst it is in the course of processing.
The generation of the high resolution video signals is effected by means of address generator 20, shape RAM 16 and patch RAM 17 shown as components Y, I, Q sections l7A, l7B, l7C. The picture point signals are applied to processor 18 (comprising section A, B and C), the results are applied to store sections l9A, l9B and l9C, the final picture is applied from 19 for reproduction in a printing scanner 21 or by other graphic process.
As the production of the image in real time progresses the generation of the high resolution video image may lag behind although if the operator is working at a slow rate the processing may catch up. The speed of processing required to keep up with the operator depends on the implement chosen, therefore patch size, and how quickly the operator is moving the stylus across the touch tablet. The final image from scanner 21 consists of an 8 bit color video image with a resolution of 2560 picture points by 2048 lines.
The system described depends for its operation on the fact the operator normally operates intermittently and may pause between strokes to examine the effect on the picture being created. Such pauses allow the high resolution processor 18 to catch up on the operator, so that the amount of buffer storage required may be held to reasonable limits. However, if the high resolution image processing lags a long way behind the real time processing then the buffer store 15 may become full and the system will no longer accept information from the touch tablet or computer. This situation may occur for example if the operator selects a mode of operation in which painting with an air brush is simulated, which may result in large areas of the picture being "painted" rapidly. If the buffer 15 becomes full the operator has to cease painting until the high resolution part of the system has processed enough information for the buffer store to be able to accept more.